Magnetic random access memory

1. A magnetic resistive element comprising: a first magnetic layer whose magnetized state changes in accordance with data; a nonmagnetic layer disposed on the first magnetic layer; and a second magnetic layer which is disposed on the nonmagnetic layer and whose magnetized state is fixed, wherein the first magnetic layer has a cross shape in which a maximum length of a first direction is L 1 and a maximum length of a second direction crossing the first direction at right angles is L 2 , and the second magnetic layer has a tetragonal shape in which the maximum length of the first direction is L 3 (≦L 1 ) and the maximum length of the second direction is L 4 (<L 2 ).

2. The magneto resistive element according to claim 1 , wherein contours of corner portions of the cross shape and the tetragonal shape can be approximated by a curvature radius R, and R has a value of 20% or less of L 1 or L 2 .

3. A magneto resistive element comprising: a first magnetic layer whose magnetized state changes in accordance with data; a nonmagnetic layer disposed on the first magnetic layer; and a second magnetic layer which is disposed on the nonmagnetic layer and whose magnetized state is fixed, wherein a ratio (L 1 /L 2 ) of a maximum length L 1 of a first direction to a maximum length L 2 of a second direction crossing the first direction at right angles in the first magnetic layer is smaller than a ratio (L 3 /L 4 ) of a maximum length L 3 of the first direction to a maximum length L 4 of the second direction in the second magnetic layer, and L 2 >L 4 .

4. A magnetic random access memory comprising: a magneto resistive element comprising a first magnetic layer whose magnetized state changes in accordance with data, a second magnetic layer whose magnetized state is fixed, and a nonmagnetic layer disposed between the first and second magnetic layers; a conductive line disposed above the magneto resistive element; and a contact pillar which connects the magneto resistive element to the conductive line, wherein at least the first magnetic layer of the magneto resistive element has a cross shape in which a maximum length of a first direction is L 1 and a maximum length of a second direction crossing the first direction at right angles is L 2 , and the contact pillar has a tetragonal shape in which the maximum length of the first direction is D 1 (≦L 1 ) and the maximum length of the second direction is D 2 (<L 2 ).

5. The magnetic random access memory according to claim 4 , wherein the nonmagnetic layer is disposed on the first magnetic layer, the second magnetic layer is disposed on the nonmagnetic layer, and both the first and second magnetic layers have a cross shape.

6. The magnetic random access memory according to claim 4 , wherein the nonmagnetic layer is disposed on the first magnetic layer, the second magnetic layer is disposed on the nonmagnetic layer, the first magnetic layer has a cross shape, and the second magnetic layer has a tetragonal shape.

7. The magnetic random access memory according to claim 6 , wherein the contact pillar has the same shape as that of the second magnetic layer.

8. The magnetic random access memory according to claim 4 , wherein the nonmagnetic layer is disposed on the second magnetic layer, the first magnetic layer is disposed on the nonmagnetic layer, the first magnetic layer has a cross shape, and the second magnetic layer has a tetragonal shape.

9. The magnetic random access memory according to claim 4 , wherein contours of corner portions of the cross shape and the tetragonal shape can be approximated by a curvature radius R, and R has a value of 20% or less of L 1 or L 2 .

10. The magnetic random access memory according to claim 4 , further comprising: a magnetic material disposed on the side surface of the conductive line, wherein a position of the bottom surface of the magnetic material is lower than that of the bottom surface of the conductive line.

11. A magnetic random access memory comprising: a magneto resistive element comprising a first magnetic layer whose magnetized state changes in accordance with data, a second magnetic layer whose magnetized state is fixed, and a nonmagnetic layer disposed between the first and second magnetic layers; a conductive line disposed above the magneto resistive element; and a contact pillar which connects the magneto resistive element to the conductive line, wherein a ratio (L 1 /L 2 ) of a maximum length L 1 of a first direction to a maximum length L 2 of a second direction crossing the first direction at right angles in at least the first magnetic layer of the magneto resistive element is smaller than a ratio (D 1 /D 2 ) of a maximum length D 1 of the first direction to a maximum length D 2 of the second direction in the contact pillar, and L 2 >D 2 .

12. A magnetic resistive element comprising: a first magnetic layer; a nonmagnetic layer disposed on the first magnetic layer; and a second magnetic layer which is disposed on the nonmagnetic layer and whose magnetized state changes in accordance with data, wherein the second magnetic layer has a cross shape in which a maximum length of a first direction is L 1 and a maximum length of a second direction crossing the first direction at right angles is L 2 , and the first magnetic layer has a tetragonal shape in which the maximum length of the first direction is L 1 .

13. The magneto resistive element according to claim 12 , wherein the maximum length of the second direction of the first magnetic layer is L 2 .